Managing weed seed rain: A new paradigm for organic and low-input farmers

Managing weed seed rain: A new paradigm for organic and low-input farmers

Summary

Modern weed management strategies continue to be focused on controlling weed seedlings, most often using herbicides or cultivation. This focus on early season weed control effectively minimizes yield loss due to weeds, but weed seed rain from individuals that survive may be extraordinary, resulting in a recurring weed problem. Furthermore, growers are frequently encouraged to plant fall cover crops, an operation that usually involves tillage and, consequently, burial of the new seed rain. Burial effectively places the weed seed in “cold storage,” offering protection from predators, and fewer environmental cues to encourage germination, a fatal process when it occurs late in the year.

The proposed project will use our current knowledge of weed seedbank ecology to evaluate the efficacy and economics of fall weed management tactics designed to maximize weed seed mortality. Specifically, we will engage ten Maine farmers in related on-farm trials focused on fall weed management strategies including: preemption of seed rain by hand hoeing/pulling, tillage, or mowing followed by fall cover cropping; managing seed rain by flail mowing for maximal presentation to post-dispersal seed predators (exclosures will demonstrate the contribution of various weed seed predator guilds); and no-till seeding of fall cover crops to maintain weed seed on the soil surface where they are exposed to weed seed predators. A replicated comparison of these treatments will be conducted at the University of Maine Rogers Farm. Case studies detailing the on-farm fall weed management trials will demonstrate to farmers throughout the region the longer-term benefits of weed control strategies that focus on the seedbank instead of solely on early season competition.

Objectives/Performance Targets

Through field days, meeting presentations, and published case studies, 150 New England vegetable and organic dairy farmers will learn about the Fall Weed Management Project; direct-mail and follow up telephone surveys will demonstrate that one third of this target audience implemented a new strategy focused on fall weed management, with 10% of the group adopting multiple tactics to preempt seed rain and maximize weed seed predation and mortality.

Evidence Performance Targets Have Been Reached

1. Attendance at on-farm site field days and grower meetings will reach an audience of over 300 mixed vegetable growers.

2. Surveys of growers in cooperation with the Maine Organic Farmers and Gardeners Association (MOFGA) and the Northeast Organic Farming Association (NOFA) will indicate the number of growers implementing strategies for weed seed rain management, and the source of their information.

3. Requests for information and on-farm visits will be used as an indicator that performance targets are being met.

4. Lastly, we will anonymously review MOFGA applications for organic certification (for growers who agree to participate in the survey) from a one- to three-year period prior to implementation of our project, and applications submitted in the fall and winter of 2008, recording the proportion of applicants implementing weed seed rain management practices.

Accomplishments/Milestones

1. Ten grower participants are selected based on individual meetings with 15 or more candidate growers.

2. On-farm tactics are selected by growers and researchers for implementation in the fall of two consecutive field seasons; tactics are implemented and maintained by project team.

3. Field days and talks at winter meetings present tactics to target audience.

4. Experiences are summarized in case studies to be published jointly by UM Cooperative Extension and the Maine Organic Farmers and Gardeners Association.

5. Surveys are conducted to document outcome.
In the fall of 2006 we established unreplicated trials at six on-farm sites, three organic vegetable operations and three organic dairy operations. Additional field sites, two organic vegetable and two organic dairy farms, will be established in the fall of 2007. These four sites were not included in the fall of 2006 due to difficulties in scheduling on-farm crop harvest and field operations, and challenging weather conditions.

An additional replicated trial including treatments included in the on-farm trials was established at the University of Maine Rogers Farm.

Impacts and Contributions/Outcomes

There was a great deal of enthusiasm for the Seed Rain Management Project among the participating farmers. The sites ranged from relatively weed-free at a recently established vegetable farm, to more than 500 grams of dry weed biomass per square meter at another vegetable farm. Growers all chose to compare no-till to tilled fall cover crops, with several additional treatments included at selected sites. Weed-free treatments were established at several sites, and cages to exclude weed seed predators were installed at all locations. One grower added a flaming treatment in an attempt to burn dry stubble and weed seeds on the soil surface.

Sites will be visited at several times in the late spring and early summer to measure weed seedling densities in the contrasting treatments, and within the seed predator exclosures. Further measurements will be made after planting and final cultivation of the subsequent crops at each location.

Collaborators: